Industrial heating, ventilation and air-conditioning (HVAC) systems often rely on gas powered combustion to produce heat. Such a system typically includes a burner or boiler to combust fuel such as natural gas. The heat from the combustion is used to heat a gas or liquid. The heated gas or liquid may be used in an HVAC system, or for some other purpose. For example, air may be directly heated and then forced through ducting. In another application, water can be heated and circulate through radiators for heating, and for other purposes (e.g., hot water for washing). Such burners may provide other functions besides HVAC, such as providing heat for manufacturing processes, co-generation of electricity, etc.
One key component on many industrial boilers and burners is a gas shutoff valve. A system may include at least one gas shutoff valve connected with a sensor or controller, such as a thermostat or thermocouple. The gas valve may be configured to open and close in response to the boiler conditions in order to maintain temperature or pressure within certain limits. Some valves are mechanically controlled by application of force or pneumatic pressure. However, an ever increasing number of these valves are electrically actuated, such as by means of a solenoid.
In many installations, the system designer or field engineer may need a valve to perform additional functions besides simply shutting off and on. For example, it may be desirable to throttle, or limit, the amount of gas flowing through the valve. An external adjustable valve may be added to the system to perform this throttling function, but the addition of a throttling valve adds cost and complexity to an installation. The connections required to add such a valve becomes another source of installation error and leaks, and may also add to inspection requirements during installation and in the future. Therefore it is desirable to provide a way to adjustably throttle a combustible fluid flow in systems such as industrial HVAC installations without installing an external throttling valve.